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Abstract:

A narrow channel is provided in the abutment mating surface of a dental
prosthesis undercase to allow excess dental cement to flow out of the
interstitial space between the dental abutment and the overlying
prosthesis. During the seating of the prosthesis the excess dental cement
is channeled to and extruded from a preferred collection point for easy
removal. Hydrostatic pressure and trapped gases that would tend to lift
the prosthesis into a non-fitting position or form a weakened cemented
bond of uneven thickness are prevented by this apparatus and method. A
positive copy of the narrow channel is attached to the lingual aspect of
the abutment analog of the model. A virtual hydrostatic groove and
lingual shelf can be subtracted from a virtual model of undercase for
manufacture using computer modeling.

Claims:

1. A dental apparatus comprising a hydrostatic groove element and lingual
shelf element having a columnar region with an external face, and sides,
and top forming a positive model of a hydrostatic relief groove; said
lingual shelf element in combination with said hydrostatic groove
element; said hydrostatic groove element and said lingual shelf element,
treated to temporarily adhere to the surface of an a dental implant
abutment, thereby becoming a hydrostatic relief groove space and a
lingual shelf relief space in an at least one abutment recess in the
undercase of the prosthesis during fabrication.

2. A dental apparatus, as in claim 1, comprising a hydrostatic groove
element and lingual shelf element having a columnar region with an
external face, and sides, and top forming a positive model of a
hydrostatic relief groove; said lingual shelf element in combination with
said hydrostatic groove element; said hydrostatic groove element and said
lingual shelf element, treated to temporarily adhere to the surface of an
a dental implant abutment analog, thereby becoming a hydrostatic relief
groove space and a lingual shelf relief space in an at least one abutment
recess in the undercase of the prosthesis during fabrication.

3. A dental apparatus, as in claim 1, comprising at least one said
hydrostatic groove element and lingual shelf element in combination
removably adhered to a carrier sheet.

4. A dental apparatus comprising a handheld tool having a left handed end
and a right handed end, said left handed end reaching a number of lingual
abutment surfaces, and said right handed end reaching a number of
opposing lingual abutment surfaces to conveniently pry and release said
abutment from said undercase of the prosthesis.

5. A dental apparatus, as in claim 1, comprising a virtual hydrostatic
groove element and virtual lingual shelf element having a virtual
columnar region with an external face, and sides, and top forming a
virtual positive model of a virtual hydrostatic relief groove and said
virtual lingual shelf element in combined with the virtual hydrostatic
groove element; said virtual hydrostatic groove element and said virtual
lingual shelf element, virtually subtracted from the undercase abutment
recess space surface, thereby becoming a hydrostatic relief groove space
and a lingual shelf relief space in an at least one abutment recess in
the undercase of the prosthesis during fabrication.

6. A dental apparatus comprising a threaded shaft having at least two
threads, said shaft threading into said implant abutment, said at least
two threads starting in at least one position to insure said hydrostatic
groove element and said lingual shelf element in combination thereby have
a compatible mating lingual surface on said implant abutment.

7. A dental apparatus, as in claim 1, comprising a virtual hydrostatic
groove element and a virtual lingual shelf element having a virtual
columnar region with an external face, and sides, and top forming a
virtual positive model of a virtual hydrostatic relief groove combined
with a virtual lingual shelf element; said virtual hydrostatic groove
element and said virtual lingual shelf element are virtually subtracted
from a virtual undercase abutment recess space surface, thereby becoming
a real hydrostatic relief groove space and a real lingual shelf space in
an at least one abutment recess in the real undercase of the prosthesis
during fabrication.

[0003] The prior disclosures of the applicant describe an apparatus and
method that acts to equitably distribute the loading forces with
retrievable dental cement between the matching surfaces of the abutments
and the internal aspect of the undercase of the final restoration. Each
abutment is made with a step or shelf on the lingual face to act as a
bearing surface for a removal instrument. The implant abutment is
modified to include a recessed shelf with enough space between the
surface of the shelf and the edge of the undercase for retrieving the
prosthesis by breaking the cemented surfaces free of each other,
eliminating the potential damage to both structures. Prior methods of
removing cemented restorations involved hammering movements under much
less control. The methods and apparatus disclosed in U.S. Pat. No.
5,564,928 in combination with an appropriate dental cement, yields a
predictable technique for securing, yet retrieving the final restoration.
Both references cited rely upon modification of the surface of the
abutment to create a parting space between the abutment and prosthesis
undercase.

[0004] Furthermore, Gittleman U.S. Pat. No. 5,897,320 taught the inclusion
of a groove in the surface of the implant abutment to act as a channel in
the directing of excess cement from within the intervening space between
the abutment and the overlying prosthesis. This channel, by allowing
excess cement to flow in a controlled manner to prearranged collection
site, prevents the capture of an incompressible mass of cement that will
hold the overlaying prosthesis in a lifted, malocclusive position. The
channel described prevents the formation of blind pockets of dental
cement that would exert an outward force and weaken the joint during
solidification of the dental cement.

BRIEF SUMMARY OF THE INVENTION

[0005] In the prior art, the hydrostatic relief channel and the recessed
shelf are formed by modifying the surface of the abutment to form a
recessed groove and shelf in the surface of the abutment itself, where
the current application modifies the internal aspect of the prosthetic
undercase. This has the commercial advantage of using unmodified
abutments from many manufacturers while taking advantage of modern
undercase manufacturing methods.

[0006] The steps of the method of replicating the hydrostatic groove and
lingual shelf are:

[0007] 1. Taking an Impression of the relevant portion of the jaw with
implant in place;

[0008] 2. Forming a cast model in stone with attached analog of the
abutment;

[0009] 3. Placing a stick-on positive model of the hydrostatic groove and
lingual shelf on the lingual aspect of the analog on the stone model; and

[0010] 4. Fabricating a model of the prosthetic undercase with a recessed
hydrostatic groove and lingual shelf in the inner lingual wall of the
internal recesses of the undercase.

[0011] Several hydrostatic relief stick-on elements can be packaged on a
sheet of material for easy removal and application to the abutment analog
with a pair tweezers, a placement tool, or the point of scalpel or an
Xacto® knife.

[0012] Advances in dentistry, which now include chair-side laser scanning
of the teeth and surrounding tissue, result in a virtual model. The
virtual model is viewed and manipulated on a computer for best fit,
proper occlusion, and structural integrity. The virtual model is then
sent as a computerized set of data to a dental laboratory for physical
construction. Since the virtual model can be added-to and subtracted-from
as virtual Boolean solids, just as if it were a physical model in the
dental laboratory, a virtual model of the hydrostatic groove and lingual
shelf can be subtracted from the inner mating surface of each mating
portion of the lingual aspect of the virtual undercase.

[0013] For the purpose of this discussion, an undercase is understood to
be the substantial bridgework mating with and joining one or more
abutment and subsequently attached to the overcase. The undercase is cast
or machined from a strength-bearing alloy or ceramic joining together
individual abutments to strengthen and support the overcase. The overcase
is the portion of the prosthesis having the aesthetic and functional
synthetic teeth. Virtual, in this context, means the computerized
equivalent list of surface points sufficiently close together to define
the surface of a physical model. The surface defines the "skin" of the
solid, much like the skin of an apple defines the surface shape of an
apple. The list of surface points in space, defining the shape of the
solid is transmitted to a laboratory for fabrication by an apparatus
controlled by this data. Inner surfaces and recesses are also defined by
this list of surface points in space.

[0014] This hydrostatic groove and lingual shelf element, as scanned, or
as placed virtually, becomes a virtual computerized hollow recess within
the inner surface of a virtual undercase substructure.

[0015] An hydrostatic groove and lingual shelf element need not physically
exist at all, if it is rendered as a "virtual" element that can be
subtracted from the inner wall of each prosthetic cavity as a placement
within the computerized model space. The computerized virtual model is
then sent to the lab to be rendered in metal by casting, milling, or
other means. The final physical undercase returned to the practitioner
has the hydrostatic relief grooves included in each undercase recess
mating with each abutment.

[0016] Thus another method of providing a hydrostatic groove and lingual
shelf comprises the following steps: [0017] 1. A scan is made of the
prepared site and surrounding region of the implant or implants. [0018]
2. The prepared site is modeled in virtual space on a computer and
displayed on the computer monitor. [0019] 3. At least one virtual model
of the hydrostatic groove and lingual shelf is moved into place in
virtual space by means of a computer mouse or other manipulation
apparatus. [0020] 4. The virtual hydrostatic groove and lingual shelf is
subtracted from the inner aspect of the lingual wall of the virtual
undercase cavity. This is repeated for each virtual undercase recess.
[0021] 5. The virtual model of the undercase of the prosthesis is
compiled into a compatible file for transmission to the dental
laboratory. [0022] 6. The dental laboratory constructs a physical
undercase from the received file.

A BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a perspective view of an abutment analog with a positive
hydrostatic groove and lingual shelf element attached;

[0024] FIG. 2 is a perspective view with a set of positive hydrostatic
groove and lingual shelf elements attached to a sheet for individual
removal and application to analogs;

[0025] FIG. 3-a, 3-b, 3-c, and 3-d, are perspective views showing an
analog, a portion of the overcase with lingual aspect visible;

[0026] FIG. 4 is a right and left handed tool for removing prosthesis;

[0027] FIG. 5 is a cross sectioned view of the abutment analog and a
portion of the overcase with recessed region created by hydrostatic
groove and lingual shelf element; And

[0028] FIG. 6 is a perspective view of a double threaded screw shaft on a
solid abutment allowing the screw to be started in one of two positions;
and

[0029] FIG. 7 is a cut away view of the double threaded screw shaft of the
solid abutment.

DETAILED DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a perspective view of a screw retained abutment 1 with
the hydrostatic groove and lingual shelf element 2 attached. The abutment
is comprised of a coronal rim 20 of a tapered conical section 16 a flared
region 14, a gingival flared region 12, and a hexagonal prism clocking
region 10. A through hole 18 for a mounting screw (not shown) retains the
abutment within an implant having a mating hexagonal recess and threaded
recess. The hexagonal prism and hexagonal recess allow the abutment to be
placed in one of six clocked positions.

[0031] A hydrostatic groove and lingual shelf element 2 is comprised of
columnar region having an external face 22 with sides 32 and 34, and top
30 forming a positive model of the hydrostatic relief groove. Lingual
shelf element 26 having a front face 28 is combined with the hydrostatic
groove element. The hydrostatic groove and lingual shelf element become a
groove and shelf in an undercase of each abutment recess in the
prosthesis. [0032] Thus this dental apparatus combines a hydrostatic
groove element and lingual shelf element having a columnar region with an
external face, sides and top forming a positive model of a hydrostatic
relief groove and a lingual shelf element combined with the hydrostatic
groove element; said hydrostatic groove element and said lingual shelf
element, treated to temporarily adhere to the surface of an a dental
implant abutment or an analog of the abutment, thereby becoming a
hydrostatic relief groove space and a lingual shelf relief space in an at
least one abutment recess in the undercase of the prosthesis during
fabrication.

[0033] FIG. 2 shows several adhesive backed hydrostatic groove and lingual
shelf elements 42 and 44 placed on a easy release sheet 40. These parts
are pick up with a scalpel or Xacto® knife, or a pair of tweezers and
attached to the lingual aspect of the abutment. [0034] Thus, this
dental apparatus combines at least one said hydrostatic groove element
and lingual shelf element in combination removably adhered to a carrier
sheet.

[0035] FIG. 3-a shows an elevated view of the mesial surface of an
abutment 1 mated with an undercase 50. The front face portion 28 of the
hydrostatic groove and lingual shelf element 2 is visible. FIG. 3-b is a
sectioned elevated view of the undercase seen from the buccal side.
Groove 58 is recessed into the inner lingual wall of the undercase.
Lingual window 60 penetrates the lingual wall at the margin 62 providing
an egress for excess cement to flow. The inner mating recess 56 fit over
an abutment allowing for a thin glue or cement interface. Outer surfaces
52 and 54 are mated with the prosthesis overcase made in a cosmetically
pleasing acrylic or porcelain. The groove and window direct excess cement
to the easily cleaned lingual region. Hydrostatic lift caused by an
excess of cement or trapped air in the cement is vented. Subsequent
removal of the undercase, if necessary for repair, is achieved by the
removal of a portion of the cement from the lingual window for the
introduction of a parting tool (See FIG. 4.) FIG. 3-c is a sectioned
elevated view of the undercase viewed from the mesial side. The
hydrostatic relief recess 58 and the shelf region 60 are formed by the
hydrostatic groove and lingual shelf element upon manufacture of the
undercase. Bridge link 64 is partly shown and is understood to connect to
other similar undercase portions 50 that mate with at least one abutment.
For a single prosthetic cap, this bridge is omitted. A typical abutment 1
is shown in FIG. 3-d having a top 18 a conical side 16 a flared shelf
region 14, and a hexagonal implant mating projection 10. In the case of a
solid abutment hexagonal projection 10 is replaced with a threaded shaft
that mates with an internal threaded recess in an implant and the
hexagonal projection is replace with a tapered cone.

[0036] FIG. 4 shows a perspective view of a handheld tool 70 for the
levered removal of a cemented overcase having at least one hydrostatic
groove and lingual window. Handle 72 has dual ends 74 and 74' with
respective offset angled regions 76 and 76' terminating in prying tips 78
and 78'. The two ends allow the practitioner to reach all lingual windows
and apply a careful twisting force to part the cement interface.

[0037] Thus, this dental apparatus comprises a handheld tool having a left
handed end and a right handed end, the left handed end reaching a number
of lingual abutment surfaces, and the right handed end reaching a number
of opposing lingual abutment surfaces to conveniently pry and release
each abutment from the undercase of the prosthesis.

[0038] FIG. 5 shows a cross section of the abutment analog 1 situated
within a recessed portion of the undercase. The conical surface 16 of the
abutment mates with conical recess surface 56 leaving a thin cement gap
64. A similar cement space 62 over the abutment analog top 18 will be
filled with cement. Any excess cement is expressed through the channel 58
and out through opening 60 in the undercase recess as the prosthesis is
seated.

[0039] FIG. 6 details a one-piece, solid body abutment 90 having, a
coronal surface 98, a conical top region 92 with an anti-rotational flat
surface 96, a conical neck region 94, and a cylindrical shaft 100 with
dual threads 102 and 104 terminating at apical end 106. Threads 102 and
104 spiral in the same direction as two parallel ridges. The starts of
each thread at the apical end 106 are 180 degrees apart. FIG. 7 details
the start of each thread 108 and 110. A matching recess with internal
dual threads located within the coronal end of a dental implant allows
the abutment to be started in two separate positions. The flat 96 will
end up in one of two diametrically opposed positions, depending upon
which abutment thread is started in which implant thread. If the abutment
threads into the implant have the flat surface 96 in a lingual position
which will interfere with the placement of the hydrostatic groove and
lingual shelf element, the abutment can be started in the opposite
implant threads. In this manner, the flat can always be repositioned away
from the lingual area. A mark or marks on the abutment can distinguish
the start of either of the two threads. A single dot can mark the
beginning of the first thread, while two dots can mark the start of the
second thread. While two threads, with diametric starts are shown, it is
understood that additional parallel threads are within the scope of this
application. Other starting angles other than 180 degrees are anticipated
by this application.

[0040] The starting points on the screw threads are at the opposite sides
of the shaft. They represent a dual thread that can be started in two
diametric positions. If a flat on single-piece abutment would fall on the
lingual side and interfere with the hydrostatic groove the thread can be
started alternately to place the flat on the opposing side. Suitable
markings on the abutment to indicate the proper clocking are also
included.

[0041] The hydrostatic groove and lingual shelf can be modeled separately
or in combination as described by applicant. Modifications to the shape
and size of the hydrostatic groove and lingual shelf element, either
singly or together, are anticipated for each style of abutment from
varying manufacturers.

[0042] It is understood that the method of manufacture of the internal
relief groove and parting shelf within at least one inner recess of the
prosthesis can be formed by one of the following processes:

[0043] A region of the mouth having implants installed is prepared with
abutments or abutment analogs. Physical positive models of the
hydrostatic groove and lingual shelf element are attached to the
appropriate lingual region of the abutment or abutment analog. An
impression is taken to allow a casting of a laboratory stone model of the
prepared region. A waxed up model of the undercase is built to create a
template for lost wax casting of the undercase. The cast undercase is
further modified with a porcelain or acrylic overcase to present an
aesthetic replica of natural teeth and gums.

[0044] A second method prepares the region of interest in the mouth with
the abutments or abutment analogs in place. Physical hydrostatic groove
and lingual shelf elements are attached to the lingual face of each
abutment or analog. An optical, three-dimensional scan is taken of the
region of interest and a virtual model of the mouth is created using
suitable modeling software on a chair side computer system having the
optical scanner attached thereto. The virtual model is then manipulated
to create a virtual model of the undercase and overcase with a
hydrostatic groove and a lingual shelf at each relevant position. The
virtual model is sent by electronic communication for fabrication.

[0045] A third method prepares the region of interest in the mouth with
abutments or analogs in place. A scan is taken to create a virtual model
If the region of interest. Virtual hydrostatic groove and lingual shelf
elements are placed on the virtual lingual aspects of each virtual
abutment or abutment analog. A virtual model of the undercase and
overcase are created including the subtraction of a virtual hydrostatic
groove and lingual shelf element from each virtual model abutment mating
recess. A physical undercase is manufactured from the coordinates of each
closely spaced point on the virtual model. The physical model can be
machined under computer control. Structural metal alloys or ceramics like
zirconia can be used. Alternately, a wax or plastic buildup of a core for
"lost wax" casting of the physical undercase can be made using "rapid
prototyping" equipment. The wax or plastic core is "burned out" of a mold
through vents and sprues and molten metal is poured into the now empty
mold cavity. Upon cooling the mold is broken apart to reveal the
undercase casting.

[0046] Since computer controlled milling apparatus has reached a level of
replication matching that of a final fit for a prosthesis, and
manufacturing facilities exist to offer a quick turn around time at
reasonable cost, this is becoming the preferred method of manufacture.
The practicing dentist, sends his scanned results, after his review and
minor modifications, all done in the virtual software realm, to a distant
laboratory as an email attachment. The laboratory constructs his
undercase (with or without the overcase) and returns a completed
prosthetic for a final installation. In the case of screw retained
abutments, the prosthesis is attached to each abutment through the
occlusal surface at each site and the hole through the occlusal surface
is repaired. A cemented prosthesis is simpler to install and with the
hydrostatic groove and lingual shelf easier to remove, if necessary.
[0047] Thus this dental apparatus comprises a virtual hydrostatic groove
element and a virtual lingual shelf element having a virtual columnar
region with an external face, and sides, and top forming a virtual
positive model of a virtual hydrostatic relief groove combined with a
virtual lingual shelf element. The virtual hydrostatic groove element and
the virtual lingual shelf element are virtually subtracted from a virtual
undercase abutment recess space surface, by software means, thereby
becoming a real hydrostatic relief groove space and a real lingual shelf
space in an at least one abutment recess in the real undercase of the
prosthesis during fabrication.